1. Field of the Invention
The present invention relates to testing mobile devices in a lab, and more particularly to techniques for testing mobile devices which incorporate characteristics of the antennas of the mobile device while bypassing the antennas.
2. Description of Related Art
When designing over-the-air (OTA) testing approaches, channel modeling concepts are applied in order to insure that the received signal is representative of the desired test condition. Most channel models such as the Spatial Channel Model (SCM) have been designed to be antenna independent, i.e. they are suitable for a variety of possible antenna arrangements. Thus the model provides a way to specify a stochastic geometric based spatio-temporal description of the paths between a base station (BS) and a mobile station (MS), such that the performance of the antennas of the base station and mobile station can be applied and modeled separately from the channel model. The base station and the mobile station will then make use of the paths in the channel model with their antenna characteristics to produce a complete end-to-end channel for evaluation and testing.
In order to include the antenna characteristics in a measurement of radio link performance using an Over-The-Air (OTA) testing techniques, it is necessary to generate and wirelessly transmit an accurate test signal such that the antennas of the device-under-test can act upon the received signal in a controlled way. For the purposes of testing, a signal to be received by the MS can be generated without requiring the BS to be present in the simulated path, or vice-versa. This is done by providing the proper signals to the transmitting and receiving elements of a portion of the channel that is being modeled. Thus a forward or reverse link transmission may be emulated.
However, generating the test signals for an over-the-air test is complex. There are multiple paths, and each path must be constructed to produce the proper correlation between antennas at the device-under-test. Thus many individual probes would typically be required to be located in a variety of positions within an anechoic chamber to produce an adequate test signal. Having many probes is costly and complex to implement. Furthermore, having many probes will degrade the characteristics of the chamber due to additional reflections that may be produced. This kind of testing is also time consuming, making it very difficult to do more than a limited set of configurations and underlying conditions.